1. Field of the Invention
The present invention relates to a methacrylimide group-containing polymer having an excellent heat resistance, fabricability, and thermal stability, and an excellent balance of these physical properties.
2. Discussion of Background
Methyl methacrylate polymers are widely used, due to their excellent transparency, weather resistance and mechanical properties, in various fields of industry such as the automobile, electrical or electronic industry, and building material. However, since the thermal deformation temperature of a methyl methacrylate polymer is as low as about 100.degree. C., it is difficult to use this polymer in an atmosphere at a temperature higher than about 100.degree. C. On the other hand, a polycarbonate has been used as a resin with a transparency and heat resistance. However, the temperature under which the polycarbonate is practically resistant is lower than 140.degree. C. Therefore, the polycarbonate is not always satisfactory according to its application.
As processes for improving the heat resistance of a methyl methacrylate polymer, there is known a process for imidizing the methyl methacrylate polymer by utilizing the side chain reaction of methyl methacrylate polymer. As the process for the imidization of a methyl methacrylate polymer, there have been proposed a process for subjecting a methyl methacrylate polymer to a thermal decomposition condensation reaction with a primary amine as disclosed in U.S. Pat. No. 2,146,209, a process for reacting a methyl methacrylate polymer with a water-soluble ammonium salt or water-soluble N-alkyl ammonium salt as disclosed in U.S. Pat. No. 3,244,679, and a process for reacting a methyl methacrylate polymer with ammonia or a primary amine in an extruder as disclosed in U.S. Pat. No. 4,246,374.
In these former processes, however, most of the imidizations are carried out by using a single imidizing agent, and thus, the imidized polymers have only one kind of methacrylimide structure. Accordingly, the polymer which is imidized with methylamine or ammonia has a low fluidity and the fabricability thereof is very poor.
On the other hand, the polymer with a low methacrylimide group content in which imidization degree is lowered to improve the fluidity has a defect that the thermal stability is low and the polymer will decompose in a high temperature atmosphere since the units of methacrylic ester and its residual derivatives remain or exist in the polymer. Thus, the polymer is not satisfactory in practical use as a heat resistant molding material.
Further, while Example 44 of the U.S. Pat. No. 4,246,374 discloses the use of a mixture of 5% ammonium and 95% butylamine as the imidizing agent, there is no specific description or suggestion of what proportion of the repeating units of methacrylimide groups and butyl methacrylimide groups formed by such imidizing agents gives the polymer an excellent heat resistance, fabricability, and thermal stability, and a good balance of these physical properties.